Atmospheric density-dependent power adjustment for wind turbines

ABSTRACT

The present invention concerns a wind power installation having a control apparatus for operational management of the wind power installation and a method of controlling a wind power installation having a control apparatus for operational management. In order to take the largest possible amount of energy from the wind the control apparatus takes into consideration the height of the location of erection of the wind power installation and/or the height of the wind power installation. The method according to the invention also detects air density, transmits signals which are derived from the air density and which represent the air density to the control apparatus, and the air density is taken into consideration by the control apparatus in operational management.

[0001] The present invention concerns a wind power installation having acontrol apparatus for operational management of the wind powerinstallation and a method of controlling a wind power installationhaving a control apparatus for operational management.

[0002] A wind power installation converts a part of the kinetic energycontained in the wind into electrical energy. For that purpose the windpower installation has a rotor which takes kinetic energy from the windand converts it into rotational energy.

[0003] DE 198 44 258 A1 discloses a wind power installation and a methodfor the operation thereof in which, in dependence on sensors, in thepresence of the air density at the wind power installation, theoperational management system sets the speed at which the wind powerinstallation shuts down at a higher level, with decreasing air density.If therefore, with a normal level of air density, the shut-down speedassumes its predetermined value, the shut-down speed is increased whenthe air density is less.

[0004] Stored in the control apparatus of a wind power installation is apower characteristic which permits the control means of the wind powerinstallation, on the basis of the ascertained rotor speed which isdependent on the wind speed, to ascertain the associated generatorpower. That generator power which the wind power installation isintended to furnish affords the exciter power required and in turntherefrom the generator moment. In order to produce that requiredgenerator moment the rotor must afford at least that rotary moment, byway of the drive train.

[0005] The power P of the wind power installation corresponds to theamount of energy flowing through the rotor circuit of the wind powerinstallation and arises out of the cross-sectional area F whichcorresponds to the circular surface area of the rotor, in accordancewith the following equation:

P=½ρv ³ F[W].

[0006] At a given wind speed v and a predetermined circular surface areaF of the rotor, the foregoing equation gives the dependency of theamount of energy on air density ρ. If the amount of energy is too lowthe rotor cannot apply that moment and therefore the rotor speed dropsas a consequence of the excessively high generator moment.

[0007] The object of the invention is to optimise operation of a windpower installation insofar as the largest possible amount of energy,that is to say the highest possible power, can always be furnished.

[0008] The object according to the invention is attained by a methodhaving the feature set forth in claim 1 and by a wind power installationhaving the feature set forth in claim 2.

[0009] In previous wind power installations, besides a characteristiccurve, the high-speed running variable λ is also predetermined. In thatrespect the high-speed running variable corresponds to the quotient ofthe peripheral speed of the rotor blade tip and the wind speed. Asalready stated, when the power characteristic is not matched to thecorresponding air density, there is a deviation in respect of thehigh-speed running variable λ which is fixed in the control apparatus.

[0010] In the present invention the control apparatus takes account ofthe height of the location of erection of the wind power installationand/or the height of the wind power installation, that is to say the airdensity which prevails at the site of the wind power installation.

[0011] The invention is based on the realisation that air densitybecomes less with increasing height. The reference scale is always sealevel normal zero (NZ). The higher the location at which the wind powerinstallation is erected is above NZ, the corresponding lower is the airdensity and the correspondingly less is the energy contained in thewind.

[0012] It is particularly advantageous in the present invention thattaking account of the height of the location of erection of the windpower installation above NZ means that this lower air density is takeninto consideration in the power characteristic. In that way the powerwhich is associated with a rotor speed and thus a given high-speedrunning variable λ and which is to be produced by the wind powerinstallation can be suitably adapted, that is to say reduced, so thatthe generator moment, as a consequence of the exciter power which isintroduced by the control apparatus, does not exceed the torque which isfurnished by way of the rotor. In that way the level of efficiency whichis established by way of the power characteristic is maintained and themaximum energy can be taken from the wind.

[0013] In a particularly preferred embodiment of the invention theheight of the location of erection of the wind power installation and/orthe height of the wind power installation can be adapted, that is to saythere can be provided a site-independent control to which theappropriate parameters can be communicated by way of suitable settingmeans such as switches, configurational parameters etc.

[0014] In a preferred development of the invention the wind powerinstallation is provided with a measuring apparatus for detecting theair density and particularly preferably a measuring apparatus fordetecting the air pressure and the temperature. The air density can bedetermined from those two items of data. In that way it is possible toforego setting the parameters as the control apparatus automaticallyascertains those parameters from the data acquired by the measuringapparatus.

[0015] In a preferred embodiment the control apparatus includes at leastone microprocessor so that control of the wind power installation can beimplemented on the basis of a control software.

[0016] In addition the object of the invention is attained by a methodwhich is characterised in that:

[0017] a) the air density is detected,

[0018] b) signals which are derived from the air density and whichrepresent the air density are transmitted to the control apparatus, and

[0019] c) the air density is taken into consideration by the controlapparatus in operational management.

[0020] In that respect in step a) the air pressure and the temperaturecan be detected and in step b) signals which represent the air densitycan be derived from the air pressure and the temperature, in accordancewith a predetermined algorithm.

[0021] Advantageous developments of the invention are recited in theappendant claims.

[0022] An embodiment of the present invention is described in greaterdetail hereinafter with reference to the FIGURE. The FIGURE shows asimplified block circuit diagram of the present invention.

[0023] The FIGURE shows the wind power installation with a rotor 10, agenerator 12, a force transmission 14 between the rotor and thegenerator, a device 16 for detecting the air pressure, a device 18 fordetecting the temperature and a control apparatus 20 with amicroprocessor.

[0024] The device 16 for detecting the air pressure is connected by wayof a connection 22 to the control apparatus 20, the device for detectingthe temperature is connected by way of a connection 24 to the controlapparatus 20 and the rotor speed is transmitted to the control apparatus20 by way of a connection 26. Those connections can be for examplegalvanic connections or other suitable connections such as wirelessconnections.

[0025] From the transmitted items of information, the control apparatus20 ascertains on the basis of predetermined power data the power whichis to be delivered by the generator and, by way of a connection 28,influences the exciter power which is fed to the generator 12.

[0026] In this respect the mode of operation of the control apparatus 20can be predetermined in such a way that changes in air density which canbe ascertained from changes in air pressure or temperature are takeninto consideration by the control apparatus 20 only when they exceed apredeterminable amount and/or those changes are ascertained for apredeterminable time.

[0027] It will be appreciated that, instead of detecting the airdensity, it is also possible to predetermine a value in respect of airdensity at the respective site. In this respect for example the heightabove NZ of the wind power installation or the rotor hub of the windpower installation is also taken into consideration. In a correspondingmanner it is also possible to predetermine a mean value in respect ofthe corresponding air density at the predetermined height and store itin the control apparatus. Accordingly the invention provides that therespective power characteristic of a wind power installation is alsoadapted to the corresponding air density at the location of the windpower installation. That makes it possible for the level of efficiencyof the wind power installation always to be maintained at the maximumpossible value, more specifically even when the air density fluctuatesto a considerable degree or the wind power installation is erected atsome hundred metres above NZ, even if the power characteristic isinitially ascertained for a site at a height of 00 above NZ.

1. A method of controlling a wind power installation comprising anelectrical generator using statistical, inputted and/or measured airdensity data at the location of the wind power installation,characterised in that the generator of the wind power installation iscontrolled by means of a control apparatus which processes the airdensity data, and power data of the generator, in particular an exciterpower supplied to the generator, are set in dependence on the airdensity.
 2. A wind power installation comprising an electrical generatorand a control device for operational management of the generator of thewind power installation, wherein there are provided means for detectingand/or setting air density data, wherein the detected and/or set airdensity data are processed in the control apparatus, characterised inthat power data with the power to be delivered by the generator of thewind power installation, in particular the exciter power supplied to thegenerator, can be set in consideration of the detected and/or set datain respect of air density.
 3. A wind power installation according toclaim 2 characterised in that there is provided a measuring apparatus(16, 18) for detecting air density, wherein the measuring apparatus isconnected to the control apparatus (20).
 4. A wind power installationaccording to claim 3 characterised in that the measuring apparatus (16,18) includes at least one device for detecting the air pressure (16) andthe temperature (18) at the site of the wind power installation.
 5. Awind power installation according to one of the preceding claimscharacterised in that the value or the data which correspond to therespective air density are predeterminable by way of input means and arestored in the control apparatus.
 6. A wind power installation accordingto one of the preceding claims characterised in that the controlapparatus includes a microprocessor in which the air density data areprocessed together with a control program of the wind powerinstallation.